1. Field of the Invention
The present invention relates to copper metal alloy that is dispersion strengthened with stable dispersed oxides and also to a method for making dispersion strengthened copper alloys.
2. Description of Related Art
It is known that the properties of ductile metals can be improved by the distribution of discrete hard phases throughout the metal matrix. Hard particles can be admixed with the metal matrix powder to form a metal having discrete hard phases dispersed therein or internal oxidation can be used to preferentially oxidize certain elements within the metal matrix.
U.S. Pat. No. 3,026,200 by Gregory discloses a method of oxidizing a metal matrix to introduce hard oxide phases into the matrix. A powder of the matrix metal having alloyed therein up to about 5% by weight of a refractory oxide forming metal is heated in an oxidizing atmosphere. The powder is then heated in an inert atmosphere to decompose surface oxides on the matrix metal and provide additional oxygen for diffusion into the powder to convert the alloying element to its oxide.
U.S. Pat. No. 3,179,515 by Grant et al. discloses the internal oxidation of alloy powders in an oxidizing environment with a partial oxygen addition, which is sufficient for the oxidation of the alloying elements of the alloy but is insufficient for the oxidation of the alloy matrix. This method permits substantially full oxidation of the alloying additives, however, it requires precise control of the oxidizing atmosphere parameters.
U.S. Pat. No. 3,525,609 by Roberts discloses a method for internally oxidizing a copper alloy. The copper alloy comprises aluminum which isoxidized to form aluminum oxide particles. The copper alloy also includes a second alloying element that does not substantially oxidize. The non-oxidizing element can include silver, cadmium or zinc.
U.S. Pat. No. 3,779,714 by Nadkarni et al. discloses a method that includes the step of melting an Al--Cu alloy, forming the alloy into a powder having a diameter of less than 300 .mu.m and mixing the alloy powder with an oxidant which consists of copper oxide with additions of aluminum oxide. The mixture of the powders is formed into briquettes and the briquettes are heated to a temperature at which the oxidant is reduced to copper, thereby releasing oxygen. The internal oxidation of the aluminum in the powder of the copper-aluminum alloy then takes place. As a result of the internal oxidation, disperse oxides of Al.sub.2 O.sub.3 distributed in the bulk of the copper are formed. The alloys, depending on the specific composition, are characterized by a strength equal to 390 MPa to 550 MPa and by a conductivity of from 78% to 92% IACS. (International Annealed Copper Standard--A copper wire 1 meter long weighing 1 gram, having a resistance of 0.15328 ohms at 20.degree. C., has a conductivity of 100% IACS)
However, the distribution of the oxidant in the bulk of the alloy powder in a sufficiently uniform manner is difficult to achieve. In areas with excessive concentration of the oxidant, unrecovered copper oxide is left after the internal oxidation. In areas with an insufficient concentration of the oxidant, the quantity of copper oxide precipitated during dissociation will be less than required for the full internal oxidation of aluminum that is soluted in the alloy. The final product will thus contain areas with unoxidized copper-aluminum solid solution. Both of these phenomena may cause a reduction of the physical and mechanical properties of the product. Further, during the preparation of the oxidant and mixing with the alloy, the contamination of the powder by the mill material and by the milled substances can occur.
U.S. Pat. No. 4,315,770 by Nadkarni (reissued as U.S. Pat. No. 31,902 on May 28, 1985) discloses a process for dispersion strengthening alloy particles by internal oxidation wherein the oxide surface film is eliminated from the surface of the matrix metal. It is disclosed that the elimination of the oxide film enhances the oxidation of the solute elements. Oxidation is carried out according to U.S. Pat. No. 3,779,714.
U.S. Pat. No. 4,315,777 by Nadkarni et al. is directed to a process for dispersion strengthening metal by internal oxidation wherein a coherent mass of alloy and oxidant is formed, such as by pressing, and is thereafter internally oxidized to oxidize the alloying elements. It is disclosed that such a method is advantageous in that it takes less force to form a blend of alloy powder and oxidant into a cohesive mass of a given percentage of theoretical density than to form dispersion strengthened metal of the same net composition into the same shape of the same density.
U.S. Pat. No. 5,004,498 by Shimamura et al. is directed to a method for dispersion strengthening a copper alloy. The raw material for the copper matrix is finely dispersed copper oxide which is dispersed with an oxide forming element such as aluminum. The mix is pulverized and heated in a reducing atmosphere to reduce the copper oxide to copper metal and oxidize the aluminum to aluminum oxide.